Hi G19276,
Regarding your plan to absorb the entire front wall and 4feet extending along the front section of the side walls, I would suggest avoiding this approach as it mimics the live-end dead-end (LEDE) room layout. The LEDE concept is something that came out of the 1970's from Don/Chip Davis/Syn Aud Con for recording control rooms. It's based on mostly ill-conceived ideas that stem from a misunderstanding of the Haas effect which describes the level at which a delayed reflection sounds equally loud to the direct sound. LEDE rooms sound very strange, they do not achieve what they claim, and to work well you need to add tons of absorption.
Have you measured the rooms frequency response yet? You can use simple test tones (RealTraps has a free and a great file from 10-300Hz) and a Radio Shack SPL meter to see where the problem frequencies lay. Doctors Toole and Olives research and philosophy with acoustical treatment is to diffuse or absorb reflections that do harm at the listening area and leave alone the ones that do potential good. Everything else can be ignored since they never arrive at the listeners' ears or if they do, they are well below the threshold of harm either in SPL or time delay or both.
The lateral reflections are beneficial - particularly in stereo - since they can produce greater apparent source width and spaciousness, while the front/rear wall reflections can decrease these attributes since they come from the same direction as the direct sound. Try putting bass traps in all 4 corners floor to ceiling and in the middle of the back wall with diffusers on either side of this centre back wall absorber. Also consider placing diffusion in the middle of the front wall (the wall behind the speakers). Side walls should be reflective or diffused at 1st reflection points unless youre into more focused imaging in which case try absorbing the first side-wall reflections. Ceiling can be either diffused or absorbed
Your 2 thick absorbers are too thin. You will need to double or triple them up to get to 4 or 6 thickness so that they behave as a broadband absorber rather than a low-pass filter that throws your speakers tonal balance off. A generous air space (e.g. 6")is also best to take their effectiveness down to lower frequencies. You need to attenuate the entire spectrum of the reflection which a 2 thick absorber wont achieve the thicker the better. Come to think of it, youre you considered using a diaphragmatic bass trap rather than the more popular fiberglass filled ones? The diaphragmatic ones hang on the wall and are about 4 thick so are not intrusive on limited floor space of your small sized rooms. They are however more costly. For diffusers for your small room you will need to use ones that you can sit closer to which means types of diffusers that dont offer temporal effects or diffuse in two directions so that only about 50% of the reflections are coming back to you. Examples of these better suited diffusers for small rooms are polyfusers (hemi-cylindrical is a better descriptor), Skyline or 2dimensional QRDs. For what its worth my room pictures show the hemis and Skylines and both are very effective.
You will also likely need parametric EQ to tame the bass peaks that are heard at the listening position and/or multiple subwoofers.
Lastly, a little education on small room physics goes a long way. Pick up Dr Floyd Tooles book and study it.
Good luck.
Regarding your plan to absorb the entire front wall and 4feet extending along the front section of the side walls, I would suggest avoiding this approach as it mimics the live-end dead-end (LEDE) room layout. The LEDE concept is something that came out of the 1970's from Don/Chip Davis/Syn Aud Con for recording control rooms. It's based on mostly ill-conceived ideas that stem from a misunderstanding of the Haas effect which describes the level at which a delayed reflection sounds equally loud to the direct sound. LEDE rooms sound very strange, they do not achieve what they claim, and to work well you need to add tons of absorption.
Have you measured the rooms frequency response yet? You can use simple test tones (RealTraps has a free and a great file from 10-300Hz) and a Radio Shack SPL meter to see where the problem frequencies lay. Doctors Toole and Olives research and philosophy with acoustical treatment is to diffuse or absorb reflections that do harm at the listening area and leave alone the ones that do potential good. Everything else can be ignored since they never arrive at the listeners' ears or if they do, they are well below the threshold of harm either in SPL or time delay or both.
The lateral reflections are beneficial - particularly in stereo - since they can produce greater apparent source width and spaciousness, while the front/rear wall reflections can decrease these attributes since they come from the same direction as the direct sound. Try putting bass traps in all 4 corners floor to ceiling and in the middle of the back wall with diffusers on either side of this centre back wall absorber. Also consider placing diffusion in the middle of the front wall (the wall behind the speakers). Side walls should be reflective or diffused at 1st reflection points unless youre into more focused imaging in which case try absorbing the first side-wall reflections. Ceiling can be either diffused or absorbed
Your 2 thick absorbers are too thin. You will need to double or triple them up to get to 4 or 6 thickness so that they behave as a broadband absorber rather than a low-pass filter that throws your speakers tonal balance off. A generous air space (e.g. 6")is also best to take their effectiveness down to lower frequencies. You need to attenuate the entire spectrum of the reflection which a 2 thick absorber wont achieve the thicker the better. Come to think of it, youre you considered using a diaphragmatic bass trap rather than the more popular fiberglass filled ones? The diaphragmatic ones hang on the wall and are about 4 thick so are not intrusive on limited floor space of your small sized rooms. They are however more costly. For diffusers for your small room you will need to use ones that you can sit closer to which means types of diffusers that dont offer temporal effects or diffuse in two directions so that only about 50% of the reflections are coming back to you. Examples of these better suited diffusers for small rooms are polyfusers (hemi-cylindrical is a better descriptor), Skyline or 2dimensional QRDs. For what its worth my room pictures show the hemis and Skylines and both are very effective.
You will also likely need parametric EQ to tame the bass peaks that are heard at the listening position and/or multiple subwoofers.
Lastly, a little education on small room physics goes a long way. Pick up Dr Floyd Tooles book and study it.
Good luck.